Yoshida - 1981 - Fundamentals of Rice Crop Science

144 FUNDAMENTALS OF RICE CROP SCIENCE
3.13. Partial productive efficiency
of nitrogen for grain
and straw production in ~~~ rice
~~~~
(drawn from Kimura and
Chiba 1943).
If very limited, nitrogen should be supplied at about 20 days before heading.
When the supply is moderate, nitrogen may be given twice — at the early growth
stages and at about 20 days before heading. When nitrogen is abundant, applications
at the early growth stages are most efficient for grain production.
Recall that about 16 kg nitrogen is required to produce 1 t rough rice in Japan and
the efficiency of nitrogen for grain production is about 62 kg grad/kg N absorbed
(see Section 3.4.6.). These values are quite comparable to those of partial productive
efficiency shown in Table 3.22.
3.7.6. Nitrogen topdressing at panicle initiation
Applying nitrogen at about 20 days before heading has a high productive efficiency
when the level is moderate or low. This period coincides with the active growth of